With the advent of the possibilities of employing optical beams as data links or information carriers, a need has arisen for devices capable of switching or deflecting optical beam for such purposes as multiplexing and demultiplexing. A variety of devices are known in the prior art for switching or deflecting optical beams such as Heidrich et al U.S. Pat. No. 3,736,045. In addition, the prior art is aware of, and has employed, the Faraday rotation or mode conversion to switch or deflect optical beams, see Pearson et al U.S. Pat. No. 3,512,867. This patent discloses an optical switching device which relies upon the Faraday rotation effect. However, the device disclosed in that patent is essentially a bulk wave device, i.e., it is relatively thick. For many reasons it is recognized that a thin-film switching device also employing Faraday rotation is preferable.
Both Tien et al. (Switching and Modulation of Light in Magneto-Optic Wave Guides of Garnet Films in Applied Physics Letter Vol. 21 No. 8, pages 394-96, Oct. 15, 1972) and Tseng et al. (Mode Conversion in Magneto-Optic Wave Guides Subjected to a Periodic Permalloy Structure, Applied Physics Letter Vol. 24 No. 6, pages 265-67, Mar. 15, 1974) recognize that mode conversion in thin-film devices is severely hampered by the differences in phase velocities for the transverse electric and transverse magnetic polarized components. Each of the articles, however, suggests increasing the mode conversion efficiency in thin-film wave guides by providing for magnetization of the optical path which is periodically reversed as a function of distance along the wave guide. Tien et al employs a serpentine patterned current conductor associated with the wave guide to generate magnetization which is periodically reversed. Tseng et al employs a periodic permalloy pattern which, in a unidirectional magnetic field provides for periodic reversal of the magnetization in the optical path.
Notwithstanding the foregoing, however, neither of these references teach a simple and effective switching device employing the periodically reversed magnetization along the optical path. Tien does mention that for switching purposes two serpentine circuits should be used, one to maximize mode conversion, when desired, and the other to inhibit conversion, when such conversion is not desired. This arrangement of two serpentine circuits will be required for each optical path and thus, in the minimum configuration necessary for a multiplexer or demultiplexer, a total of four such serpentine circuits are required along with the attendant apparatus to energize and deenergize the circuits at the proper times. Although such a solution appears to be operative, it has a disadvantage of requiring unnecessary apparatus and the current conductors closely associated with the wave guides can cause undesirable heating of the wave guide at operating current levels.